diff --git a/source/libs/nodes/src/nodesCodeFuncs.c b/source/libs/nodes/src/nodesCodeFuncs.c
index a76a5fa07188c72ed6dc73bce5b7cebdbe94b3db..9e3608ec1a99530bded1029abe71f532af13c8af 100644
--- a/source/libs/nodes/src/nodesCodeFuncs.c
+++ b/source/libs/nodes/src/nodesCodeFuncs.c
@@ -2177,7 +2177,7 @@ static int32_t jsonToDatum(const SJson* pJson, void* pObj) {
         code = TSDB_CODE_OUT_OF_MEMORY;
         break;
       }
-      varDataSetLen(pNode->datum.p, pNode->node.resType.bytes);
+      varDataSetLen(pNode->datum.p, pNode->node.resType.bytes - VARSTR_HEADER_SIZE);
       if (TSDB_DATA_TYPE_NCHAR == pNode->node.resType.type) {
         char* buf = taosMemoryCalloc(1, pNode->node.resType.bytes * 2 + VARSTR_HEADER_SIZE + 1);
         if (NULL == buf) {